Orifice Flow

This calculation implements the following standards:

  • AGA 3 Part 4 (2003)

  • ISO 5167-2 (2003)

Only flange tappings are supported at present.

The following limits apply:

  • Differential pressure ≥ 0

  • Density > 0

  • Viscosity > 0

  • Isentropic Exponent ≥ 1

Values will be calculated for diameter ratios between 0.1 and 0.9, which is wider than the range strictly permitted by either standard.

The upstream pressure less the DP must not give a negative downstream pressure.


This area contains some calculations related to flow measurement.  They are not certified accurate within 0.001% and may not be the latest editions, but they are usable for general work.  Scroll down or click a link on the left to find a calculation. Enter values, select units, and then click the relevant Calculate button.


Please take a little care with your input.  Initial or trailing whitespace is OK.  Input is evaluated up to the first invalid character, including embedded spaces.  Exponential format such as 1.01e-3 works as long as there is no space before the "e" or anywhere else.  Some result fields can be entered, but will updated when you click Calculate.


The value of gas constant used here is 8.31451 J/(mol K),  as recommended in ISO-6976 and American Gas Association Report #8.  There are other, slightly different values in common use.

The web host does not allow pop-ups, so error reporting is rather crude.  Values with problems are highlighted, and usable values sometimes substituted.



The contents of this area is provided "as-is" for general use.  No warrantee is expressed or implied.  Please use the "Contact Us" page to report any problems you may notice.


Gas PTZ Calculation

This is a simple PTZ gas density calculation - ideal gas density plus compressibillty factor, Z.  Select the required Output Value, fill in the other values, and click Calculate.  The compressibility factor allows adjustment for non-ideal behaviour - set it to 1.0 for an ideal gas.


Please go to the top of the page for some help and the usual disclaimers.


Pipe Flow

Select the inputs and units you prefer, and click Calculate.  The values that you did not enter will be updated as far as possible.  The formula for the Reynolds Number is adjusted according to the chosen entry data, so it will update on the bare minimum of input values (for example, velocity + diameter + kinematic viscosity).